1. Field of the Invention
The present invention is directed to a method and to an apparatus for matching at least one visualized medical measured result with at least one further dataset containing spatial information, by means of landmarks.
2. Description of the Prior Art
It has long been standard in many medical fields to visually present measured results of a test subject such as, for example, a human body or a part thereof. For example, x-ray exposures are a very simple example of this. The advantage of visually presented measured results is that their content can be easily and quickly grasped, to allow a fast evaluation and a simple comparison of the measured results.
Measured results that are acquired with modern electronic measurement systems, and thus that are usually in digital form, are often edited by computer and visually presented—for example, on a monitor or with a printer. Examples of such electronic measurement systems that are currently in widespread use are computed tomography systems and magnetic resonance tomography systems.
A particular advantage of visualized measured results that are in digital form is that these are accessible for digital data processing, and thus can be edited further with suitable computational operations, for example with a computer.
The measured results can be nearly arbitrarily enlarged, reduced in size, turned, tilted, etc. by digital manipulations. Further, digital measured results can be analyzed and manipulated with suitable algorithms. A simple example of such manipulation is the coloring of certain characteristic regions of a visualized measured result.
Due to the above advantages, visualized measured results (for example, conventional x-ray images) that are usually not originally in digital form are digitized, for example with a scanner, in order to make them accessible for digital data processing.
Recently, a considerably need has arisen as a consequence thereof with respect to the further-processing of such visualized measured results.
Thus, for example, it is desirable to match a number of visualized measured results of a test subject that were registered with different measuring instruments, at different points in time with the same measuring instrument or from different observation positions, for the purpose of a comparative analysis. Matching with a reference measured result (for example, the visualized measured result of a healthy organ) can also be of interest.
A typical field of employment of this, in addition to diagnostics, is minimally invasive surgery.
In diagnostics, for example, it can be desirable to superimpose a current, visualized measured result of a test subject such as, for example, a body part of a patient, with another visualized measured result of the same test subject at some other point in time in order to be able to easily identify changes/trends.
A superimposition with a visualized reference measured result (that, for example, shows a healthy organ) or some other dataset containing a spatial information also can be of interest.
In particular, the superimposition of visualized measured results makes it possible to combine the intensities of different measuring devices/measuring methods. For example, a tumor identified with a measuring method of x-ray diagnostics could be combined into a visualized measured result produced by a measuring method of magnetic resonance tomography.
Another advantage of matching visualized measured results is that a uniform measured result for the entire test subject can be acquired from a number of visualized measured results of a part of the test subject under consideration that are registered in overlapping fashion, by suitable superimposition of the visualized measured results.
It is often necessary in minimally invasive surgery to remotely control the movement of probes and to thereby solve complex navigation tasks. It is of particular advantage when a visualized measured result of the momentary position of a probe, be determined with a first measuring instrument (for example, a digital x-ray apparatus), can have a visualized measured result of the same test subject registered with a different medical apparatus (for example, a magnetic resonance tomography apparatus) or registered from a different observation angle superimposed on it.
Such a matching in the form of a superimposition is desirable not only in two-dimensional space but also in n-dimensional space.
Problems in the matching of different visualized measured results particularly occur due to different alignments and distortions, but also arise due to different scalings of the visualized measured results to be considered.
For solving this problem, it is known to implement a matching of a number of visualized medical measured results of a test subject by means of landmarks.
The basic principle of this known method is explained below on the basis of FIGS. 5 and 6 with reference to the example of two visualized medical measured results to be matched:
In a first step S10, a first landmark E1 is defined in a first visualized measured result E.
In a second step S20, a switch is made to another visualized measured result E′ of the same test subject MO.
In a third step S30, a landmark E1′ is defined at a corresponding point of the visualized measured result E′. For orientation, one can make use of the test subject MO shown in the visualized measured results E, E′.
The points E1 and E1′ thus form a point pair that is defined from the outset.
Although the landmarks can be fundamentally defined at arbitrary points in the visualized measured result, it is advantageous to select characteristic points of the test subject MO shown in the visualized measured results E, E′ as landmarks, so that points can be selected for a point pair that always correspond to one another in the various visualized measured results.
Subsequently, a check is made in step S40 to determine whether an adequate number of point pairs have already been defined. For a two-dimensional matching, at least two are usually required and at least three point pairs are usually required for a three-dimensional matching.
If the check in step S40 shows that an adequate number of point pairs have not yet been defined, then a switch is made back to the first visualized measured result E in step S50, and the method is continued in step S10 with the definition of a further landmark E2 in the first visualized measured result E.
If the check in step S40 shows that an adequate number of point pairs have been defined, then the method continues with step S60 wherein the two visualized measured results are matched by placing the landmarks E1, E1′, E2, E2′, etc., forming a point pair on top of one another.
It is disadvantageous in the aforementioned method that the landmarks forming a point pair always must be placed by pairs in the visualized measured results, since the reference between the landmarks would otherwise be lost. Thus, one must constantly change back and forth between the visualized measured results being observed. Accordingly, the known method is very complicated, and thus it is often not possible for a physician in the operating room to implement a matching arrangement as required, for example, for navigation tasks), of a newly acquired, visualized medical measured result on site.
German Patent 196 39 615 discloses a reflector referencing system for surgical and medical instruments as well as a marker system for body portions to be treated neural-surgically. This known apparatus has at least two cameras and a computer unit connected to the cameras, and also has a radiation source for infrared radiation and a reflector group having at least two reflectors for this infrared radiation. The reflectors are attached to the instruments or treatment apparatus in an arrangement that is characteristic of only this reflector group. The known referencing system thus functions with passive reflectors secured to the patient or to the treatment table.
An apparatus for the implementation of medical interventions and a method for generating an image are disclosed in German OS 198 46 687. According to this known apparatus, first image data acquired pre-operatively are updated with second image data acquired intra-operatively, namely according to the changes between two second image data registered at different points in time. A calibration device is provided for this purpose, which is attached rigidly to the body of a patient and has at least one landmark which represents a fixed, common reference point for the first and second image data with reference to the body. Such a device allows, for example, matching image data obtained with ultrasound immediately before the beginning of the operation with image data obtained pre-operatively by means of computed tomography or magnetic resonance tomography, this being carried out by a so-called “co-registration”. Preferably, a stereotactic identifier is employed as the landmark. Further, German OS 198 46 687 discloses a method that includes the steps of storing first image data of the body acquired, for example, by means of computer tomography or magnetic resonance tomography, registering second image data of the body, for example with ultrasound, at a first point in time and at a second point in time following the first point in time, comparing the second image data registered at the first and at the second points in time to one another, updating the first image data according to the change deriving from the comparison, and displaying the updated, first image data. The first point in time and the position of the body in the registration of the second image data are selected such that the second image data registered at the first point in time correspond to the stored, first image data. In other words, a calibration has to be undertaken by matching the first and the second image data to one another to be sure they reproduce one and the same condition of the body.